1. Field of the Invention
The invention relates to a supercharging system and a diagnostic method for a supercharging system.
2. Description of Related Art
As a supercharging system that is applied to an internal combustion engine, there is a supercharging system that supercharges an internal combustion engine by utilizing exhaust energy, that is, a so-called turbocharger. A supercharging system of this type includes a compressor and a turbine that drives the compressor. The compressor is installed in an intake passage of the internal combustion engine. The compressor pressurizes intake air flowing through the intake passage, and discharges the pressurized intake air to a combustion chamber of the internal combustion engine. The turbine is installed in an exhaust passage of the internal combustion engine. The turbine is operated by the stream of exhaust gas flowing through the exhaust passage, and drives the compressor. In addition, a supercharging system of this type may include a bypass passage and a waste gate valve for actively controlling the supercharging operation of the supercharging system. The bypass passage is a passage that bypasses the turbine and allows exhaust gas to flow. The waste gate valve interrupts flow of exhaust gas through the bypass passage when fully closed, and allows flow of exhaust gas through the bypass passage when opened.
Japanese Patent Application Publication No. 09-004507 (JP 09-004507 A) describes a technique for diagnosing whether a waste gate valve has an abnormality, such as locking. In JP 09-004507 A, a supercharging pressure during supercharging and a supercharging pressure during non-supercharging are compared with each other, and, when the difference between those supercharging pressures is smaller than a value that is estimated during normal times, it is determined that the waste gate valve is locked. In this way, whether the waste gate valve is locked is diagnosed.